4673589
Description
Mind Map by Emily Sutton, updated more than 1 year ago
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Created by Emily Sutton
about 8 years ago
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Meiosis
- most organisms are diploid (2n) with 2 copies of each
chromosome (homologous pair) one from each parent
- humans have 23 homologous pairs
giving total of 46 chromosomes
- gametes haploid with only alf number of
chromosomes/ DNA present
- when gametes fuse in sexual reproduction
the diploid number is restored
- when gametes fuse in sexual reproduction
the diploid number is restored
- gametes haploid with only alf number of
chromosomes/ DNA present
- humans have 23 homologous pairs
giving total of 46 chromosomes
- Meiotic stages I
- INTERPHASE I
- dna content doubled and new
cell organelles formed
- dna content doubled and new
cell organelles formed
- PROPHASE I
- 1) chromosomes become shorter and thicker 2) homologous
chromosomes pair up as a bivalent 3) each chromosome is two
chromatids and crossing over between homologous
chromosomes with formation of chiasma 4) centrioles move to
opposite ends of nucleus, microtubules form asters and then the
spindle 5) nuclear envelope breaks and nucleolus disappears
- 1) chromosomes become shorter and thicker 2) homologous
chromosomes pair up as a bivalent 3) each chromosome is two
chromatids and crossing over between homologous
chromosomes with formation of chiasma 4) centrioles move to
opposite ends of nucleus, microtubules form asters and then the
spindle 5) nuclear envelope breaks and nucleolus disappears
- METAPHASE I
- bivalents align on the equator attached to spindle. Maternal
and paternal chromosomes are arranged randomly
- bivalents align on the equator attached to spindle. Maternal
and paternal chromosomes are arranged randomly
- ANAPHASE I
- whole chromosome (centromere do not
split) move to the poles. each one of the
random paternal or maternal homologous
pair moves to opposite pole by
contraction of spindle fibres
- whole chromosome (centromere do not
split) move to the poles. each one of the
random paternal or maternal homologous
pair moves to opposite pole by
contraction of spindle fibres
- TELOPHASE I
- animal cell : cytokinesis may
occur or plants: may go
straight onto meiosis II
- animal cell : cytokinesis may
occur or plants: may go
straight onto meiosis II
- INTERPHASE I
- Meiotic stages II
- PROPHASE II
- new spindles form at right
angles to the old spindle
- new spindles form at right
angles to the old spindle
- METAPHASE II
- chromosomes line up at
spindle equator attached
to centromere
- chromosomes line up at
spindle equator attached
to centromere
- ANAPHASE II
- centromeres divide and sister
chromatids pulled to opposite poles
- centromeres divide and sister
chromatids pulled to opposite poles
- TELOPHASE II
- 1) chromosomes lengthen and become indistinct
2) spindle disappears 3) nuclear membrane
reforms 4) cytokinesis
- four haploid cells
produced (eg.
sperm/eggs)
- four haploid cells
produced (eg.
sperm/eggs)
- 1) chromosomes lengthen and become indistinct
2) spindle disappears 3) nuclear membrane
reforms 4) cytokinesis
- PROPHASE II
- meiosis can generate variation
- RANDOM ASSORTMENT
- independent segregation of maternal
and paternal homologous
chromosomes in metaphase I
- independent segregation of maternal
and paternal homologous
chromosomes in metaphase I
- CROSSING OVER
- occurs in prophase I with the formation of
chiasmata (so get different combinations of alleles
when genetic information is exchanges)
- occurs in prophase I with the formation of
chiasmata (so get different combinations of alleles
when genetic information is exchanges)
- RANDOM
FERTILISATION
- of many genetically different haploid
gametes
- of many genetically different haploid
gametes
- RANDOM ASSORTMENT
- Meiosis is the reduction division producing gametes in sexually reproducing organisms (diploid 2n to haploid n cells)
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